Slurry wall grabs or cutters produce narrow trenches or open cuts with a depth up to 80 m. As a function of the particular use, the trench width is typically 300 mm to 1500 mm. The slurry wall means is lowered by device of a supporting cable into the trench produced and oriented and positionally stabilized by a lateral guide frame. The dimensions of the guide frame roughly correspond to the cross-section of an opened shovel or scoop of a slurry wall grab or the cutting wheel arrangement of a slurry wall cutter.
Normally precisely vertical trenches can be produced. However, there is sometimes a need to diverge slightly from the vertical in order to meet special demands. It is therefore important in such cases that the slurry wall device can be directionally controlled to a certain extent, so as to be able to perform direction corrections or changes. Such a control can be initiated in the case of a grab by a pivoting of the grab spades. For this purpose it is necessary to turn the bearing block with the grab spades mounted thereon with respect to the overall structure of the slurry wall grab. As a result, a direction change can be obtained and also a possible divergence from the given, vertical trench orientation can be corrected. Such a device is set forth in either JP-A-560 077 423 or DE-C-3602 387.
Another direction control possibility exists by constructing parts of the guide frame in a displaceable or slidable manner, so that by a planned displacement or deflection of parts of the guide frame and the interaction thereof with the walls of the trench, there is a planned tilting of the slurry wall means. The use of these so-called control flaps is set forth in either DE-A-38 05 868 or DE-C-41 19 212.
These two possibilities for the direction control of a slurry wall grab are further set forth in EP 412 477 B1.